LaCrosse (LAC) virus, an arbovirus of the California group, will be studied in its natural hosts the mosquito Aedes triseriatus and the chipmunk Tamias striatus to determine if either host selects for virus variants. Unpassaged field strains will be inoculated into chipmunks and then maintained by alternate infection of mosquitoes and chipmunks. Large and small plaques will be harvested from chipmunk blood and from mosquito saliva; virus from each harvested plaque will be tested for mouse neurovirulence, mosquito infectivity, temperature stability, and antigenic character. Results will be analyzed for possible differences between virus grown in mosquitoes and that grown in chipmunks, as well as between virus from large placques and from small plaques. Further studies of LAC virus in wildlife will concentrate on red foxes (Vulpes fulva). Their large home ranges and wandering habits make them candidates for virus transport and thus for reintroduction and mixing of virus variants which may have developed in isolated wood lots. Studies to evaluate red foxes as LAC hosts will begin with growth curves of experimentally infected animals and surveys for antibody in foxes trapped in enzootic areas. BIBLIOGRAPHIC REFERENCES: Ksiazek, T.G., and T.M. Yuill. In press. Viremia and antibody response to LaCrosse virus in sentinel gray squirrels (Sciurus carolinensis) and chipmunks (Tamias striatus). Am. J. Trop. Med. Hyg. 1977. Ksiazek, T.G., and T.M. Yuill. In press. Selection of LaCrosse virus variants by sentinel squirrels (Sciurus carolinensis) and chipmunks (Tamias striatus) Acta. Virol. 1977.